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Thomas McDougall, J. Edwin Dickinson, David R. Badcock; Battenberg summation reveals larger psychophysical receptive fields for motion signals. Journal of Vision 2014;14(10):290. doi: https://doi.org/10.1167/14.10.290.
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© ARVO (1962-2015); The Authors (2016-present)
Classic area summation studies increase the overall size of the stimulus to increase signal area. The results of this approach can be obfuscated by summation of additional internal noise as stimulus size increases. This study re-evaluated summation extent for motion signals using a Battenberg stimulus (Meese, 2010) designed to circumvent internal noise changes by holding display size constant. In the checkerboard stimulus, the size of the checks containing signal (3 cycles/deg luminance-modulated drifting sinewave gratings) can be varied to measure dependence on signal area. Experiment 1 used either, signal checks alternating with uniform, mean luminance, checks (single-motion condition), or alternate checks containing gratings moving in opposite directions (opposing-motion condition). The latter tests whether summation extent changes when segregating regions based on motion direction. Contrast thresholds for motion detection were measured using a 2IFC task in conjunction with adaptive staircase procedures in four observers, for a range of check sizes (0.7째 to 3.2째). Results show summation over an area of at least 3.2째 in size and this was found for both motion combinations, providing no evidence that the summation extent differs when segregating patterns based on motion direction, at the absolute detection threshold. However, high-contrast stimuli increase surround suppression (Tadin, Lappin & Blake, 2003). Therefore, Experiment 2 employed a suprathreshold, 20% contrast, pedestal in the signal checks in both intervals of the 2IFC; a contrast discrimination task. The aim was to determine whether differences in summation extent arise when segregation processes become more active. The results showed no dependence on check size, thus no evidence of summation for either the single-motion or opposing-motion stimulus for contrast discriminations well above threshold, across the range of sizes tested. This supports findings that motion summation diminishes at high-contrast, but provides no evidence that summation extent is dependent on motion combination, at suprathreshold levels.
Meeting abstract presented at VSS 2014
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